Polyurethanes are produced by reacting a polyisocyanate and an organic polyol in the presence of a catalysts and optionally a blowing agent and a surfactant, and further optionally other auxiliary agents such as a crosslinking agent. Of those polyurethanes, flexible polyurethane foams are lightweight and superior in elasticity, and hence, are widely used for products such as vehicles, furniture, beddings, and cushions. Of the flexible polyurethane foams, hot mold foams are mainly used in the field of automobile cushions, and slab foams are mainly used in the fields of furniture, beddings, and cushions.
In general, in the slab foams and hot mold foams, good foams are produced by using, as a catalyst, tin-based catalysts in combination with amine catalysts. Especially, the use of the tin-based catalysts is inevitable from the standpoints of curing properties and molding processing. The tin-based catalysts generally used are stannous dioctoate, dibutyltin dilaurate, etc. The polyol generally used are cheap general-purpose polyols prepared by adding propylene oxide (hereinafter referred to as “PO”) to glycerin as an initiator. Formerly, in the production of low-density foams, Freon compounds such as CFC-11 had been used as a blowing agent. However, it was pointed out that the Freon compounds likely break an ozone layer, and there were provided severe controls in the use of Freon compounds in the world. Accordingly, in recent years, there has been employed a method of use of methylene chloride in combination with water as a replacement of the Freon compounds. However, with respect to methylene chloride, adverse influences against the environment and toxicity are also pointed out. Thus, there has been proposed a method for using only water as the blowing agent, or a method for using carbon dioxide as the blowing agent.
In addition to the improvement of the blowing agent, there is also demanded an improvement of the catalyst system. That is, in the tin-based catalysts, trace amounts of highly toxic dibutyltin and the like are incorporated as impurities, and these impurities cannot be removed. Thus, it is pointed out that when the tin-based catalysts are used, highly toxic chemical substances consequently remain in the urethane foam. In addition to the toxicity problem, there is also pointed out a problem that the tin-based catalysts is poor in storage stability in a premix so that it is difficultly stored over a long period of time. In view of these problems, it is eagerly demanded to develop formulations from which slab foams or hot mold foams can be produced without using the tin-based catalysts.
In addition, in the conventional formulations, it is generally employed to use general-purpose tertiary amine catalysts such as triethylenediamine and N-ethylmorpholine in combination with the tin-based catalysts. However, the tertiary amine-based catalysts and the like remain in a free form in polyurethane resin products and are discharged as a volatile amine step-by-step, resulting in various problems. For example, the volatile amine discharged from the polyurethane products introduces an odoriferous problem. Also, in recent years, there is a so-called fogging problem such that the volatile component in polyurethane foams attaches to a windshield of an automobile and fogs the windshield, resulting in causing a reduction of commercial values. Besides, there are other problems such as a problem in which the volatile amine discharged from polyurethane products contaminates other materials. Thus, it is also demanded to improve these problems generated when the general-purpose catalysts are used.
However, in the case where a flexible polyurethane foam is formed from a polyol as a major raw material by eliminating a tin-based catalysts from the conventional formulation using a general-purpose polyol (a polyol obtained by adding only PO to glycerin) and using the conventionally used general-purpose amine catalysts such as triethylenediamine, N,N-dimethylaminoethanol, and N-ethylmorpholine, there occur serious problems such that the foam formation becomes instable; defoaming (collapse of foams) occurs; and even when foams can be formed, cracks are likely generated in the foam, whereby satisfactory air flow is not obtained, and therefore, foams having superior physical properties cannot be obtained.
There is a method of using a highly reactive polyol having an oxyethylene group introduced into terminals of the polyol chain thereof in place of the conventional polyol. In this case, there is a problem that a ratio of closed cells in the foam is high. As a result, the air flow of the foam becomes remarkably worse, leading to problems such as shrinkage of the foam.
In addition, in order to solve the odoriferous problem and the fogging problem generated in the use of the general-purpose amine catalysts, there is proposed a method of using so-called reactive amine catalysts containing an amino group or a hydroxyalkyl group in the molecule thereof. However, in the case where foams are formed by eliminating the tin-based catalysts from the conventional formulations and using only the reactive amine catalysts, the foam formation becomes more instable as compared with the case where only the general-purpose catalysts is used, and therefore, good foams cannot be obtained. Further, of the reactive amine catalysts, a part of the amine catalysts may be possibly volatilized. Accordingly, the odoriferous problem and the fogging problem cannot be solved unless proper reactive amine catalysts are used.